Bark processing



1962 E. EBERHARDT BARK PROCESSING Filed May 7, 1958 -10 QMEMQQQ mmskwszMQQEEDM xttm kmB United States Patent Ohio Filed May 7, 1958, Ser. No.733,606 5 Claims. (Cl. 1107) This invention relates to methods ofmaterial handling and treatment, allied to the art of reducing woodplant stock to a pulp form for paper making and like purposes. Moreparticularly, the invention is concerned with a method of treatment andutilization of by-products of the plant reduction process, especiallytree bark.

In pulping processes as described, logs are stripped of their bark as apreliminary step since the essentially superficial character of the barkmaterial prevents it from being successfully combined with the woodfibers. Through various processes of soalc'ng, abrading and the like,most of the bark is removed before the wood is placed in process. Atvarious points in the course of treatment of the wood, and the fibers ofwhich it is composed, additional action is taken to cleanse or to removefrom the fibrous material particles of bark which escaped the originalstripping. The bark has heretofore been essentially a waste product andits handling and disposal long hasposed a problem. Some effort has beenmade to burn it, elther solely for the sake of disposal or as a fuel toproduce steam useful to provide power and in the cooking of Wood fibers.These efforts have had inconsistent results, however, mainly because thebark contains a high percentage of water and often will barely supportits own combustion. Thus, and in spite of the fact that dry bark isknown to have a high heat potential (tests having indicated that onepound of dry bark can provide seven to eight pounds of steam) there hasbeen prior to the present invention no economically feasible system forthe advantageous use of bark as a fuel.

The instant invention has in View a method of handling bark material toachieve a successful and economically sound use thereof as a fuel.

The object of the invention is to sirnphfy the construction as well asthe means and mode of operation of bark -of applications, and beunlikely to get out of order.

A specific object of the invention is to conduct raw bark material to afurnace in a more or less continuous process in the various steps ofwhich the bark is finally sub-divided ard thoroughly dried.

Another object of the invention is to obtain a drying and sub-dividingof wet bark material through use of known refining equipment and withoutneed for supplemental heat.

A further object of the invention is to make use of the residue ofliquor extracted from wet bark material as a fuel, combined in thefurnace with the dried and divided bark material whereby to utilize theknown high B.t.u. content of such residue as well as to relieve streampolution.

A further object of the invention is to provide a bark processing meanspossessing the advantageous structural features, the inherentmeritorious characteristics and the mode of operation herein mentioned.

With the above and other incidental objects in view as will more fullyappear in the specification, the invention intended to be protected byLetters Patent consists of the features of construction, the parts andcombinations thereof, and the mode of operation as hereinafter de-3,064,592 Patented Nov. 20, 1962 scribed or illustrated in theaccompanying drawings, or their equivalents.

The drawing is a diagram of a system in accordance with the illustratedembodiment of the invention, showing the apparatus used in the method ofhandling and treating the bark material and its route followed in theflow through such apparatus.

Referring to the drawing, wet bark is introduced in a raw state, as itcomes from debarking and like machines, into means such as a hammer mill10 where it undergoes an initial reduction to a divided state productiveof a more readily handled mass of material. Thus, raw bark of varyingshapes and sizes is fed into the mill 10 and subjected to thedisintegrating action of rotary hammers 11 operable within a cylinder 12and acting to force particles of the bark from the cylinder by way ofopenings 13 therein. The expelled particles, along with the liquidreleased or still contained therein, are confined by casing 14 anddirected into a suitable conveying means which conducts them to theinlet 15 of a press refiner 16.

The device 16, known heretofore for treatment of wood fibers, isarranged to receive the discharge from the hammer mill 10, to which maybe added other rejects from the plant stock. The bark and these rejects,hereinafter referred to generally as bark material, enters the device 16at one end of a power driven feed screw like element 17 by which it isprogressively advanced to an outlet 18 at the opposite end of thedevice. The feed screw 17 cooperates with conical and sharp edged damformations in surrounding relation thereto to apply to the material inits progress through the press refiner a high degree of compression andpowerful shearing forces, these forces of shearing and compression beingalternated and progressively increased in intensity in such manner thatthe bark material emerges from the press refiner in a sub-dividedcondition and relatively dry. The liquid expressed from the barkmaterial in its progress through the press refiner drains into the lowerpart thereof and then is conducted as indicated to an evaporator 19. Theliquid with which the bark material normally is impregnated is in themain water. Within the press refiner 16, however, and due to thepowerful forces of compression and disintegration which are exerted, thereleased liquid carries with it some of the essence of the bark materialand so flows to the evaporator 19 as a liquor.

Within the evaporator 19, heat is applied in a suitable manner to boiloff the water in the liquor directed thereto. There remains a residuewhich is known to have a high heat value. This residue may as indicatedbe connected directly to a furnace 21 and there burned as a fuel, itbeingunderstood that the furnace 21 represents a part of a steam makingunit variously used in a reduction plant of the kind with which theinstant invention has an allied use.

The press refiner 16 dries the bark material to a range of 50 to 70percent of a bone dry condition and, as noted, sub-divides the material.It accordingly emerges from the outlet 18 in a relatively dry, looseform composed of comparatively small particles so that it is in areadilyflowable condition. In this state, the bark material'is directedto the open inlet 22 of an attrition mill 23. Within the mill 23, thebark material enters a chamber 24 within which is a pair of relativelyrotatable grinding discs 25 and 26. Within the chamber 24, the barkmaterial is compelled to pass between the discs 25 and 26 and then leavethe chamber by way of an outlet 27 in the bottom thereof. In its passagebetween the discs, the bark material further is subdivided, beingreduced therein to a fineness similar to powdered coal. The reduction ofthe bark material between the relatively rotating discs 25 and 26 beingessentially a friction and abrading action there is a resulting heatgeneration raising the temperature of the discs and of the barkmaterial. Also, the increased reduction of the bark material adds to theamount of surface area which the bark material presents for contact withsurrounding air. ,As a result of this combination of circumstances afavorable condi' tion is established for the flashing or yielding up ofmoisture from the bark material to the surrounding air. Air is free toenter the chamber 24 by way of inlet 22, and, according to a feature ofthe invention, additional air inlets are provided at 29 and 31 in theupper part of the chamber. The admitted air, as well as the reduced barkmaterial are carried off by way of the outlet 27 and under the urging ofan exhaust type fan 32. Operation of the fan 32, it will be understood,has the effect of rapidly and thoroughly evacuating the chamber 24 andat the same time induces a forced draft of replacement air into thechamber by way of the inlet 22 and openings 29 and 31. Thus, the heatingand fine dividing of the bark material takes place in the presence offlowing air so that as the air immediately surrounding the bark materialbecomes saturated or moisture laden it is replaced by fresh, relativelydry air. In this connection, it further will be understood that the airsupplied to the attrition mill 23 for passage through the chamber 24 maybe controlled as to its source in order that it may be warmed and driedin preparation for its passage through the mill. The bark material, nowreduced to a powder-like consistency and in effect suspended in moistureladen air, is directed by the fan 32 to a cyclone separator 33. Inaccordance with the known operation of devices of this kind the streamof moisture laden air in which the bark material is suspended isdirected into the separator 33 at the upper end thereof and travels in,a helical path toward the lower or apex end thereof. During the process,the relatively light air moves toward the longitudinal axis of thedevice and rises for discharge from the open upper end, in the mannerindicated. The heavier particles, which in this instance comprise thebark material, drop through the bottom of the separator unit, theirmovement being assisted by a fan 34. The fan .34 discharges as indicatedinto the furnace 21 so that the bark material is combined with theresidue'from evaporator 19 and burns to fire the furnace. The thoroughlydried and powdered bark has, like the residue from evaporator 19, a highheat value, it being calculated that a system as disclosed provides8,000 to 10,000 B.t.u. per pound of bone dry bark or provides five toseven pounds of steam per pound of bark.

It will be understood that modifications may be made in the system asdisclosed without departing materially from the invention. Thus, the wetbark material may be broken up initially in any convenient manner, as byhand or manually. In the interest of abatement of pollution, and toprovide a readily combustible residue material, the evaporator 19 servesa useful purpose, but the liquor expressed from the bark material by thepress refiner 16 could be discharged to waste. Also, the cycloneseparator 33 results in the supplying of the bark material, to thefurnace in the form of a relatively solid fuel. The air suspended barkcould, however, be blown directly from the attrition mill into thefurnace hearth for flash burning in suspension.

From the above description it will be apparent that there is thusprovided a device of the character described possessing the particularfeatures of advantage before enumerated as desirable, but whichobviously is susceptible of modification in its form, proportions,detail construction and arrangement of parts without departing from theprinciple involved or sacrificing any of its advantages.

While in order to comply with the statute the invention has beendescribed in language more or less specific as to structural features,it is to be understood that the invention is not limited to the specificfeatures shown, but that the means and construction herein disclosedcomprise but one of several modes of putting the invention into effect,and the invention is therefore claimed in any of its forms ormodifications within the legitimate and valid scope of the appendedclaims.

Having thus described my invention, I claim:

1. A method of providing fuel for a furnace from wet bark consisting ofthe steps of reducing the bark to a if divided state and extractingliquid therefrom by applying shearing and squeezing forces thereon,conducting the extracted liquid through an evaporator and reducing it toa combustible bark residue and further sub-dividing and drying the barkmaterial and thereby simultaneously producing both the combustible barkresidue and the dried sub-divided bark material in the form offuel'having a high heat potential.

2. A method of providing fuel for a furnace from wet bark consisting ofthe steps of reducing the bark to a divided state and extracting liquidtherefrom in the process by applying shearing and squeezing forcesthereon, conducting the extracted liquid to an evaporator and reducingit to a combustible bark residue therein, further reducing the shearedand squeezed bark material to a powder form and drying the powdered barkmaterial in the process whereby to provide both a combustible barkresidue and a dried powdered bark material having a high heat valueadapting it for use as a fuel.

3. A method of processing wet bark to provide fuel including the stepsof subjecting initially divided bark material to successive shearing andsqueezing forces in a press refiner whereby to sub-divide and partly drythe bark material by extracting a substantial portion of the.

liquid therefrom in the process, subjecting the sub-divided barkmaterial to the action of an attrition mill or the like to reduce it toa powder-like consistency and discharging the powder-like bark materialfrom said mill in the presence of a forced draft of air in a manner tocause the powder-like bark material to yield up remaining moisture at anaccelerated rate.

4. A method according to claim 3 characterized by the further step ofpassing the powder-like bark material and the moisture laden airresulting through a cyclone separator or the like to effect a dischargeof a completely dry compressible finely divided powder-like barkmaterial having a high heat value.

5. A method according to claim 3 characterized by converting theextracted liquid and reducing it so as to leave a combustible residue inthe form of a liquor from the bark material having a high heatpotential.

References Cited in the file of this patent UNITED STATES PATENTS425,603 Fleischman Apr. 15, 1890 2,271,157 Badenhausen I an. 27, 19422,303,811 Badenhausen Dec. 1, 1942 2,481,305 Fuller Sept. 6, 1949

